Friday, January 25, 2008

Differential gene expression can make a difference in morphology

This study is the first to show it (abstract below). These researchers put part of an enhancer of the gene Prx1 from a bat into mice, and they find that the mice displayed longer forelimbs, albeit only 6% longer. Theoretically, this could be an example of one step out of many small ones on the way towards developing the ability for flight.Another interesting finding was that when they deleted the Prx1 enhancer in the mouse, they didn't find any immediate effects on forelimb length, "revealing regulatory redundancy", according to the authors.

Abstract: Natural selection acts on variation within populations, resultingin modified organ morphology, physiology, and ultimately theformation of new species. Although variation in orthologousproteins can contribute to these modifications, differencesin DNA sequences regulating gene expression may be a primarysource of variation. We replaced a limb-specific transcriptionalenhancer of the mouse Prx1 locus with the orthologous sequencefrom a bat. Prx1 expression directed by the bat enhancer resultsin elevated transcript levels in developing forelimb bones andforelimbs that are significantly longer than controls becauseof endochondral bone formation alterations. Surprisingly, deletionof the mouse Prx1 limb enhancer results in normal forelimb lengthand Prx1 expression, revealing regulatory redundancy. Thesefindings suggest that mutations accumulating in pre-existingnoncoding regulatory sequences within a population are a sourceof variation for the evolution of morphological differencesbetween species and that cis-regulatory redundancy may facilitateaccumulation of such mutations.